The present invention broadly relates to a new and improved method for fabricating a substantially dished or pot-shaped hollow body possessing straight or helical inner or internal toothing or teeth. The method is especially well suited, although not exclusively, for the fabrication of internal geared wheels or gears for use in planetary gear trains or system.
Generally speaking, the method of the present invention for fabricating from a blank of a workpiece a substantially dished or pot-shaped hollow body possessing straight or helical inner or internal toothing or teeth, which hollow body possesses an at least partial web portion or dish base and a tubular rim portion or dish rim connected to the web portion or dish base, as present in the case of an internal geared wheel or gear of a planetary gear system, comprises the steps of cold forming or cold working, according to the widely known Grob method or process, the rim portion or dish rim of the blank of the workpiece on a mandrel which possesses an outer or external toothing or teeth corresponding to the inner . or internal toothing or teeth to be fabricated at the substantially dished or pot-shaped hollow body.
In order to avoid any misunderstandings from the outset, the widely known Grob method of cold forming or cold working will be briefly elucidated hereinafter, even though this method is well known in this particular technology or art from documentation as well as from practice:
In the Swiss publication which is entitled "Industrie-Anzeiger", 95 (1973), No. 20, Page 393, there is disclosed that the Grob process can be used to produce relatively thin-walled, tubular parts which are equipped with similar toothings or teeth on the inside and the outside.
A special development of the Grob method which permits the fabrication of relatively thick-walled workpieces is disclosed in Swiss Patent No. 579,427, in French Patent No. 7,538,539 and in the German Patent No. 2,549,230, to which reference may be readily had and the disclosure of which is incorporated herein by reference. With these methods, different toothings or gear tooth systems can be fabricated on the inside and the outside of the workpiece.
In both of the above cases, an outer or external toothing or teeth and an inner or internal toothing or teeth are simultaneously fabricated by cold forming or cold working. The tubular workpiece is mounted on a suitable mandrel or plug. This mandrel has an outer or external toothing or teeth which corresponds to the inner or internal toothing or teeth of the workpiece which is to be fabricated. The workpiece mounted on the appropriate mandrel has imparted thereto an axial feed by axially moving and rotating the workpiece about its lengthwise axis. During the workpiece feed, the workpiece is externally worked by annular or ring-like profiled forming rolls or rolling tools (shaped in conformity with the outer or external toothing or teeth), whereby each forming roll or rolling tool performs single or individual blow-like or impacting forming operations in rapid succession or sequence. The site of application or locality of these single or individual blow-like or impacting forming operations performed at the workpiece is synchronized with or accommodated to the pitch of the toothing or teeth and the feed of the workpiece. These single blow-like or impacting forming operations are carried out in the same sense of direction and predominately in the lengthwise direction of the toothing or teeth. The single or individual blow-like impacting or forming operations consecutively carried out by the same forming roll or rolling tool lie in a helical or screw-like zone. This helical or screw-like zone is determined by the feed of the workpiece. Seen in the lengthwise direction of the toothing or teeth, the individual, consecutive blow-like or impacting forming operations in the same tooth gap or space partially overlap each other as concerns their point of application at the workpiece. During each single blow-like or impacting forming operation, material is pushed along a relatively small section of the workpiece into one of the depressions of the mandrel, mainly flowing in a radial direction.
Even in the case of the Grob method, a good shaping or forming of the inner or internal toothing or teeth is sometimes a problem, particularly with relatively thick-walled products, and substantially dished or pot-shaped or dish-like hollow bodies are particularly difficult to handle.
Also significant to the Grob method or process is German Patent No., 1,016,222, published Sept. 26, 1957, the disclosure of which is incorporated herein by reference.